1. Field of Invention
The present invention relates to voltage booster circuits and voltage boosting methods which reduce the number of charge-accumulating devices required for a voltage boost and electronic units using the output of such a voltage booster circuit as a power source.
2. Description of Related Art
In liquid-crystal display apparatuses, for example, a high-voltage power source is required to drive liquid-crystal devices in order to obtain successful display characteristics. Therefore, a power-source circuit used in the liquid-crystal display apparatuses is configured such that an input voltage is boosted by a voltage booster circuit and the boosted voltage is supplied to a driving circuit for driving the liquid-crystal devices and to other circuits.
The configuration of a conventional voltage booster circuit will be described below for a case in which a voltage-boost magnification set to four is taken as an example. FIG. 13 is a circuit diagram showing the configuration of a voltage booster circuit 138 in this case. The voltage booster circuit 138 is formed of transistors Q1 to Q8, auxiliary capacitors C1, C2, and C2p, and an output capacitor Cout.
FIG. 14 is a timing chart of control signals sent to the voltage booster circuit 138. A control signal xe2x80x9caxe2x80x9d shown in this figure is generated by narrowing the pulse width of a control signal xe2x80x9cb,xe2x80x9d and is sent to n-channel transistors Q2, Q4, Q6, and Q8 in the voltage booster circuit 138 as gate signals. A control signal xe2x80x9cbxe2x80x9d is supplied to p-channel transistors Q1, Q3, Q5 and Q7 of the voltage-booster circuit 138 as the gate signal.
When the control signals xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d are sent to the voltage booster circuit 138, transistors Q2, Q4, Q6, and Q8 are turned on whereas the other transistors are turned off in a period indicated by {circle around (1)} in FIG. 14, that is, a period in which only the control signal xe2x80x9caxe2x80x9d has an xe2x80x9cHxe2x80x9d level. Therefore, the auxiliary capacitor C1 is charged with an input voltage Vin since a terminal C1H is connected to the supply line of the input voltage Vin and a terminal C1L is connected to the ground line, as shown in {circle around (1)} of FIG. 15. The auxiliary capacitor C2 is connected in parallel to the auxiliary capacitor C2p charged with 2 Vin, in a period indicated by {circle around (2)}, and is charged. After these operations, all the transistors Q1 to Q8 are turned off temporarily.
In a period indicated by {circle around (2)} in FIG. 14, that is, a period in which both control signals xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d have an xe2x80x9cLxe2x80x9d level, transistors Q1, Q3, Q5, and Q7 are turned on whereas the other transistors are turned off. Therefore, as shown in {circle around (2)} of FIG. 15, since the terminal C1L of the auxiliary capacitor C1 is switched and connected to the supply line of the input voltage Vin and the terminal C1H is disconnected from the supply line of the input voltage Vin, the potential of the terminal C1H becomes 2 Vin, which is offset from the input voltage Vin to a higher potential by the output voltage Vin of the auxiliary capacitor C1. On the other hand, since a terminal C2pH of the auxiliary capacitor C2p is connected to the terminal C1H, the auxiliary capacitor C2p is charged with a potential difference of 2 Vin. Therefore, the potential of the terminal C2pH becomes 2 Vin in the period ‡A. In addition, since the terminal C1H is connected to a terminal C2L of the auxiliary capacitor C2, which has been charged with 2 Vin in the period ‡A, the potential of the terminal C2H of the auxiliary capacitor C2 becomes 4 Vin, which is offset from the potential of the terminal C1H (C2pH, C2L), 2 Vin, to a higher potential by the output voltage 2 Vin of the auxiliary capacitor C2. And then, the potential is smoothed by the output capacitor Cout. With the periods {circle around (1)} and {circle around (2)} being repeated in this way, the input voltage Vin is boosted four times and outputted.
To increase the voltage-boost magnification, for example, to set the voltage-boost magnification to 16, seven auxiliary capacitors C1, C2, C2p, C3, C3p, C4, and C4p are used, as shown in FIG. 16. As shown in {circle around (1)} of the figure, the auxiliary capacitor C1 is charged with an input voltage Vin, the auxiliary capacitor C2 is connected in parallel to the auxiliary capacitor C2p which has been charged with 2 Vin in {circle around (2)} and is charged, the auxiliary capacitor C3 is connected in parallel to the auxiliary capacitor C3p which has been charged with 4 Vin in {circle around (2)} and is charged in the same way, and the auxiliary capacitor C4 is connected in parallel to the auxiliary capacitor C4p which has been charged with 8 Vin in {circle around (2)} and is charged in the same way.
As shown in {circle around (2)} of the figure, the auxiliary capacitor C2p is first charged with 2 Vin, which is offset from the input voltage Vin to a higher potential by the output voltage Vin of the auxiliary capacitor C1; secondly, the auxiliary capacitor C3p is charged with 4 Vin, which is offset from a potential of 2 Vin caused by the auxiliary capacitor C1 to a higher potential by the output voltage 2 Vin of the auxiliary capacitor C2; thirdly, the auxiliary capacitor C4p is charged with 8 Vin, which is offset from a potential of 4 Vin caused by the auxiliary capacitor C2 to a higher potential by the output voltage 4 Vin of the auxiliary capacitor C3; and fourthly, a potential of 16 Vin, which is 16 times the input voltage Vin, is obtained by offsetting a potential of 8 Vin caused by the auxiliary capacitor C3 to a higher potential by the output voltage 8 Vin of the auxiliary capacitor C4.
In the conventional voltage booster circuit, however, if the smoothing capacitor Cout is excluded, three capacitors are required for a four-times voltage boost and seven capacitors are required for a 16-times voltage boost. Generally, (2nxe2x88x921) capacitors are required for a 2n-times voltage boost. When a power-source circuit including a voltage booster circuit is integrated, it is difficult to form capacitive circuits such as capacitors on a semiconductor substrate. Even if such a capacitive circuit can be formed, since it makes the circuit size larger, the number of capacitors required for a voltage boost needs to be reduced as much as possible.
The largest problem in the conventional voltage booster circuit is that it is difficult to control the voltage-boost magnification as required. Therefore, to make the boosted voltage constant at the desired voltage value, a separate constant-voltage circuit such as a switching regulator is required at a later stage in the voltage booster circuit, and accordingly, the scale of the power-source circuit becomes large.
The present invention provides a voltage booster circuit and a voltage boosting method which allow the number of charge-accumulating devices required for a voltage boost, such as capacitors, to be reduced to simplify the configuration and which allow the voltage-boost magnification to be controlled relatively freely. The invention also provides an electronic unit using the output of the voltage booster circuit as a power source.
To achieve the foregoing, a voltage booster circuit according to the present invention may include a first connector for connecting one terminal of a first charge-accumulating device to a first line having a predetermined potential and for connecting the other terminal of the first charge-accumulating device to a second line having a potential different from that of the first line, a second connector for connecting one terminal of a second charge-accumulating device to the first line, and for switching and connecting the one terminal of the first charge-accumulating device to the second line and for switching and connecting the other terminal of the first charge-accumulating device to the other terminal of the second charge-accumulating device, and a third connector for switching and connecting the one terminal of the second charge-accumulating device to the other terminal of the first charge-accumulating device and for switching and connecting the other terminal of the second charge-accumulating device to an output line.
According to the present invention, since the first charge-accumulating device is connected between the first and the second lines, the other terminal of the first charge-accumulating device has the same potential as the second line when it is assumed that the first line has a reference potential. When the one terminal of the first charge-accumulating device is switched from the first line to the second line, since the potential of the other terminal of the first charge-accumulating device is offset from the potential of the second line in the potential direction opposite to that to the first line by the output voltage of the first charge-accumulating device, which is twice the potential of the second line, and the second charge-accumulating device is charged therewith. When the one terminal of the second charge-accumulating device is switched from the first line to the other terminal of the first charge-accumulating device, and the other terminal of the second charge-accumulating device is switched from the other terminal of the first charge-accumulating device to the output line and connected, the potential of the output line becomes four times the potential of the second line, which is offset from the potential of the other terminal of the first charge-accumulating device, having a potential that is twice the potential of the second line, in the potential direction opposite to that to the first line by the output voltage of the second charge-accumulating device. Therefore, two charge-accumulating devices are required to boost the potential difference between the first and the second lines four times, and thus the configuration is simplified. In other words, although charge-accumulating devices, such as capacitors need a large area when integrated and are difficult to form, since the number of required charge-accumulating devices is reduced according to the present invention, the configuration can be simplified. Such a configuration can be used in a case when the first line has a higher potential than the second line as well as in a case when the first line has a lower potential than the second line. The reference potential may be the potential of the first line or that of the second line.
It is preferred that the voltage booster circuit according to the present invention further include a fourth connector for connecting the one terminal of the second charge-accumulating device to the first line and for connecting the other terminal to the second line, and a controller for exclusively controlling the connection of the second charge-accumulating device established by the second connector and the connection of the second charge-accumulating device established by the fourth connector.
With this configuration, if the controller controls such that the connection period of the second charge-accumulating device established by the second connector is set to the entire period and the connection period of the second charge-accumulating device established by the fourth connector is set to zero, the potential of the output line becomes four times the potential of the second line as described above. On the other hand, if the controller controls such that the connection period of the second charge-accumulating device established by the second connector is set to zero and the connection period of the second charge-accumulating device established by the fourth connector is set to the entire period, since the output voltage of the second charge-accumulating device becomes equal to, not two times, the potential difference between the first line and the second line, the potential of the output line becomes three times the potential of the second line. Therefore, when the potential of the output line is smoothed with the connection-period ratio being controlled, the voltage-boost magnification can be varied to any value between three and four.
In this case, it is preferred that the controller control such that the connection period of the second charge-accumulating device established by the second connector is longer than the connection period of the second charge-accumulating device established by the fourth connector when the potential of the second line or a potential according to the output line is lower in absolute values than a predetermined value. With this control, the potential of the output line can be made constant between three times and four times the potential of the second line.
It is preferred that the voltage booster circuit according to the present invention further include a fifth connector for connecting the other terminal of the first charge-accumulating device to the output line while the one terminal of the first charge-accumulating device is being connected to the second line, and a controller for exclusively controlling the connection of the second charge-accumulating device established by the second or fourth connector and the connection established by the fifth connector.
With this configuration, if the controller controls such that the connection period of the second charge-accumulating device established by the second or the fourth connector is set to the entire period and the connection period of the second charge-accumulating device established by the fifth connector is set to zero, the potential of the output line becomes four times or three times the potential of the second line as described above. On the other hand, if the controller controls such that the connection period of the second charge-accumulating device established by the second or the fourth connector is set to zero and the connection period of the second charge-accumulating device established by the fifth connector is set to the entire period, the output line has the same potential as the other terminal of the first charge-accumulating device, having a potential that is two times the potential of the second line. Therefore, when the potential of the output line is smoothed with the connection-period ratio being controlled, the voltage-boost magnification can be varied to any value between four and two, or between three and two.
In this case, it is preferred that the controller control such that the connection period of the second charge-accumulating device established by the second or fourth connector is longer than the connection period established by the fifth connector when the potential of the second line or a potential according to the output line is lower in absolute values than a predetermined value. With this control, the potential of the output line can be made constant between four times and two times, or between three times and two times the potential of the second line.
In addition, it is preferred that the voltage booster circuit according to the present invention further include a sixth connector for connecting the second line to the output line, and a controller for exclusively controlling the connection of the second charge-accumulating device established by the second or fourth connector or the connection established by the fifth connector, and the connection established by the sixth connector.
With this configuration, if the controller controls such that the connection period of the second charge-accumulating device established by the second or the fourth connector or the connection period established by the fifth connector is set to the entire period and the connection period established by the sixth connector is set to zero, the potential of the output line becomes four times, three times, or two times the potential of the second line as described above. On the other hand, if the controller controls such that the connection period of the second charge-accumulating device established by the second or the fourth connector or the connection period established by the fifth connector is set to zero and the connection period of the second charge-accumulating device established by the sixth connector is set to the entire period, the output line has the same potential as the second line. Therefore, when the potential of the output line is smoothed with the connection-period ratio being controlled, the voltage-boost magnification can be varied to any value between four and one, between three and one, or between two and one.
In this case, it is preferred that the controller control such that the connection period of the second charge-accumulating device established by the second or fourth connector or the connection period established by the fifth connector is longer than the connection period established by the sixth connector when the potential of the second line or the potential according to the output line is lower than a predetermined value in absolute values. With this control, the potential of the output line can be made constant between four times and the same as the potential of the second line, between three times and the same as the potential of the second line, or between two times and the same as the potential of the second line.
To achieve the foregoing, a voltage booster circuit according to the present invention has at least n (n being an integer of three or greater) charge-accumulating devices and may include a first connector for connecting one terminal of a first charge-accumulating device to a first line having a predetermined potential and for connecting the other terminal of the first charge-accumulating device to a second line having a potential different from that of the first line, a second connector for connecting one terminal of a second charge-accumulating device to the first line, and for switching and connecting the one terminal of the first charge-accumulating device to the second line and for switching and connecting the other terminal of the first charge-accumulating device to the other terminal of the second charge-accumulating device, a third to n-th connectors for connecting one terminal of a m-th (m being an integer satisfying 3xe2x89xa6mxe2x89xa6n) charge-accumulating device to the first line, and for switching and connecting the one terminal of the (mxe2x88x921)-th charge-accumulating device to the other terminal of the (mxe2x88x922)-th charge-accumulating device and for switching and connecting the other terminal of the (mxe2x88x921)-th charge-accumulating device to the other terminal of the m-th charge-accumulating device, and an (n+1)-th connector for switching and connecting the one terminal of the n-th charge-accumulating device to the other terminal of the (nxe2x88x921)-th charge-accumulating device and for switching and connecting the other terminal of the n-th charge-accumulating device to an output line.
Assuming that xe2x80x9cnxe2x80x9d is set to four, for example, since the first charge-accumulating device is connected between the first and the second lines, the other terminal of the first charge-accumulating device has the same potential as the second line. Then, when the one terminal of the first charge-accumulating device is switched to the second line, the potential of the other terminal of the first charge-accumulating device is two times the potential of the second line, and the second charge-accumulating device is charged therewith. Then, when the one terminal of the second charge-accumulating device is switched to the other terminal of the first charge-accumulating device, the potential of the other terminal of the second charge-accumulating device becomes four times the potential of the second line, and the third charge-accumulating device is charged therewith. Then, when the one terminal of the third charge-accumulating device is switched to the other terminal of the second charge-accumulating device, the potential of the other terminal of the third charge-accumulating device becomes eight times the potential of the second line, and the fourth charge-accumulating device is charged therewith. Then, when the one terminal of the fourth charge-accumulating device is switched to the other terminal of the third charge-accumulating device, the potential of the other terminal of the fourth charge-accumulating device becomes 16 times the potential of the second line. Therefore, when xe2x80x9cnxe2x80x9d is set to four, four charge-accumulating devices are required to boost the potential difference between the first and the second lines 24=16 times, and thus the configuration is simplified. In other words, when xe2x80x9cnxe2x80x9d is set to an integer of three or more, n charge-accumulating devices are required to boost the potential difference between the first and the second lines 2n times, and especially when xe2x80x9cnxe2x80x9d is set to a large integer, the present invention is convenient to simplify the configuration.
In addition, to achieve the foregoing, a voltage boosting method according to the present invention may include a first step of connecting one terminal of a first charge-accumulating device to a first line having a predetermined potential and of connecting the other terminal of the first charge-accumulating device to a second line having a potential different from that of the first line, a second step of connecting one terminal of a second charge-accumulating device to the first line, and of switching and connecting the one terminal of the first charge-accumulating device to the second line and of switching and connecting the other terminal of the first charge-accumulating device to the other terminal of the second charge-accumulating device, and a third step of switching and connecting the one terminal of the second charge-accumulating device to the other terminal of the first charge-accumulating device and of switching and connecting the other terminal of the second charge-accumulating device to an output line.
In the same way, to achieve the foregoing, a voltage boosting method according to the present invention using at least n (n being an integer of three or greater) charge-accumulating devices may include a first step of connecting one terminal of a first charge-accumulating device to a first line having a predetermined potential and of connecting the other terminal of the first charge-accumulating device to a second line having a potential different from that of the first line, a second step of connecting one terminal of a second charge-accumulating device to the first line, and of switching and connecting the one terminal of the first charge-accumulating device to the second line and of switching and connecting the other terminal of the first charge-accumulating device to the other terminal of the second charge-accumulating device, a third to n-th steps of connecting one terminal of a m-th (m being an integer satisfying 3xe2x89xa6mxe2x89xa6n) charge-accumulating device to the first line, and of switching and connecting the one terminal of the (mxe2x88x921)-th charge-accumulating device to the other terminal of the (mxe2x88x922)-th charge-accumulating device and of switching and connecting the other terminal of the (mxe2x88x921)-th charge-accumulating device to the other terminal of the m-th charge-accumulating device, and an (n+1)-th step of switching and connecting the one terminal of the n-th charge-accumulating device to the other terminal of the (nxe2x88x921)-th charge-accumulating device and of switching and connecting the other terminal of the n-th charge-accumulating device to an output line.
Furthermore, to achieve the foregoing, an electronic unit according to the present invention may include a first connector for connecting one terminal of a first charge-accumulating device to a first line having a predetermined potential and for connecting the other terminal of the first charge-accumulating device to a second line having a potential different from that of the first line, a second connector for connecting one terminal of a second charge-accumulating device to the first line, and for switching and connecting the one terminal of the first charge-accumulating device to the second line and for switching and connecting the other terminal of the first charge-accumulating device to the other terminal of the second charge-accumulating device, and a third connector for switching and connecting the one terminal of the second charge-accumulating device to the other terminal of the first charge-accumulating device and for switching and connecting the other terminal of the second charge-accumulating device to an output line, and a potential according to the output line is used as a power source.
In the same way, to achieve the foregoing, an electronic unit according to the present invention has at least n (n being an integer of three or greater) charge-accumulating devices, may include a first connector for connecting one terminal of a first charge-accumulating device to a first line having a predetermined potential and for connecting the other terminal of the first charge-accumulating device to a second line having a potential different from that of the first line, a second connector for connecting one terminal of a second charge-accumulating device to the first line, and for switching and connecting the one terminal of the first charge-accumulating device to the second line and for switching and connecting the other terminal of the first charge-accumulating device to the other terminal of the second charge-accumulating device, a third to n-th connector for connecting one terminal of a m-th (m being an integer satisfying 3xe2x89xa6mxe2x89xa6n) charge-accumulating device to the first line, and for switching and connecting the one terminal of the (mxe2x88x921)-th charge-accumulating device to the other terminal of the (mxe2x88x922)-th charge-accumulating device and for switching and connecting the other terminal of the (mxe2x88x921)-th charge-accumulating device to the other terminal of the m-th charge-accumulating device; and an (n+1)-th connector for switching and connecting the one terminal of the n-th charge-accumulating device to the other terminal of the (nxe2x88x921)-th charge-accumulating device and for switching and connecting the other terminal of the n-th charge-accumulating device to an output line, and a potential according to the output line is used as a power source.